Fibrous materials and processes for making same



2,730,478 Patented Jan. 10, 1956 2,730,478 FIBROUS MATERIALS AND PROCESSES FOR MAKING SAME William A. Morgan, Jr., Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 5,1954, Serial No. 414,516

7 Claims. (Cl. 154-101) This invention relates to the manufacture of sponge, chamois-like and leather-like products, and to processes for forming such products from nylon fibers.

Both natural and man-made or synthetic fibers have been formed into non-woven structures by addition of adhesive materials. Thermoplastic fibers and blends of thermoplastic fibers and non-thermoplastic fibers may be formed into non-woven sheets at temperatures and pressures high enough to soften or fuse the thermoplastic fibers which serve as a binder for the non-thermoplastic fibers. If either of these treatments is extended sulficiently to give the high degree of interfiber bonding required in materials of high tensile and tear strength, the products become undesirably stiff and boardy for many uses. Efiorts to manufacture materials having the admirable qualities of leather (e. g. high vapor permeability, tensile and tear strengths, flexibility and scuif resistance) have been noteworthy for their failure to produce a 7 product excelling in all these qualities.

The present invention provides an answer to the problem of devising leather-like structures and also teaches the production of two novel intermediates having the characteristics of sponge and chamois. The utility of the products described below is readily apparent from the These and other objects will be readily apparent from the description that follows.

According to the present invention sponge-like fibrous batt coherent, partially destroying the discontinuity between individual fiber surfaces.

fibrous structure is quite spongy, being compressible and resilient and capable of taking up many times its weight of heat and pressure. Much stronger leather-like products can be formed by a different modification of the sponge structure. In this modification, the sponge is subjected to a treatment of nitric acid which retracts or shortens the end-to-end length of the fibers. duces a stronger and more coherent structure of considerably smaller areas than the original batt.

Fibers treatable according to this invention may be designated broadly as nylon, such as, e. g., the diaminedibasic acid condensation products described in U. S. Patents 2,130,948, 2,071,250 and 2,071,253.

aqueous bath. Example I illustrates the sponge formation.

compressing, the modified nylon structure was washed in water.

removed by squeezing in a manner similar to a conventlonal sponge.

A novel modification of the sponge structure can be elfected by hot pressing while (1 Example [I d respect. it could be torn apart by hand with the exertion of moderate force.

Example 111 A scuff-resistant leather-like product was made from a piece of sponge formed as described in Example I. It was immersed in aqueous 22.8% nitric acid solution at room temperature for one minute, by which time it lost 40% of its original area. It was washed, dried, and hot pressed for two minutes at 100 C. and 500 p. s. i. The product, which was about 0.04 inch thick, was extremely tough, scuff-resistant and appeared only slightly fibrous to the eye. Despite the compactness of this structure, it was highly permeable to water vapor. The liquid water take-up of this product was only a small fraction of that of the materials described in the above examples.

Example IV A water vapor permeable leather-like product was made as follows: A needle loomed batt weighing about 8 ounces per square yard and composed of 3 denier, 4%. inch nylon staple fibers was immersed in warm (4050 C.) aqueous 60% zinc chloride solution for about one minute. The wet batt was subjected to light pressure while wet. It was then washed with water to remove residual Zinc chloride and then dried. The batt was next immersed in aqueous 23% nitric acid solution at about C. for about one minute. Immediately upon immersion in the nitric acid bath the batt lost about of its original area. While wet with the nitric acid bath the batt was subjected to light pressure. After washing with water to remove residual nitric acid the batt was dried and subjected to a pressure of 500 p. s. i. at 110 C. for about one minute.

The permeability of the final product to water vapor was 8,000 to 12,000 grams per 100 square meters per hour. This compares very favorably with the minimum water vapor permeability value of 2,000 grams per 100 square meters per hour, which is necessary for comfortable shoe uppers. The water vapor permeability of finished shoe uppers rarely exceeds 10,000 grams per 100 square meters per hour, under the above test conditions.

The water vapor permeability test was carried out as follows: A 3 inch diameter crystallizing dish, filled with 12 mesh calcium chloride, is covered with a membrane of the substance under test, and suspended inverted in an atmosphere of high humidity (23 C. and 90% relative humidity). The assemblage is weighed at intervals and the equilibrium rate of sorption recorded as grams of water per 100 square meters of surface per hour. This is a modification of a test for water vapor permeability developed by the Bureau of Standards---Kanogy & Vickers, J. Res. Nat. Bur. of Stds., 44, 347-62, 1950 (Apr.).

Example V A fiuffy loosely bound batt of 3 denier, 1 /2 staple nylon fibers weighing approximately 8 ounces per square yard was formed on a Rando Webber. The batt was immersed in an aqueous solution of zinc chloride bath at 50 C. for two to three minutes and while still wet lightly pressed. After removal of the batt from the aqueous zinc chloride bath, the excess solution was allowed to drain. The batt was next washed with water to remove as much of the remaining solution as possible and then dried. The zinc chloride treatment increased the mechanical strength of the batt sufficiently that it could be handled without danger of disruption or distortion. The batt had a spongy character as in the case of Example 1.

After the nylon batt was treated with the zinc chloride, washing and drying, it was divided into five parts and each part was immersed in an aqueous 23% nitric acid bath for about one minute at five different temperatures. As soon as the nylon batts were immersed in the nitric acid rapid shrinkage of the batt took place; the speed and degree of shrinkage being dependent on the concentration and temperature of the nitric acid bath. After immersion in the nitric acid bath the batts were washed with water and dried. The following table illustrates the effect the difierent temperatures of the nitric acid bath had on the zinc chloride treated batt:

Percent Shrinkage of Original Area of Batt Temperature of Aqueous 23% Nitric Acid Bath, O.

The batts treated with the aqueous 23% nitric acid bath at the different temperatures were all fibrous and leather-like. They were somewhat stiffer than calf skin leather. The treated batts may be softened to a condition approaching that of calf skin by padding them in a 3:1 sulfonated castor oil-glycerine mixture and then pressing at elevated temperatures.

in place of the sulfonated castor oil-glycerine mixture, sulfonated castor oil alone, methyl-IO-phenylol stearate or sulfonamides may be used as the softening agent. To further enhance the appearance and surface characteristics of the leather-like products they may be treated by spraying with an aqueous 1015% solution of phenol at about C. A final hot pressure treatment of the phenol treated batt with a smooth plate or roller produces a very smooth surface having much improved resistance to abrasion without adversely affecting the breathability of the leather-like product. In place of a smooth plate or roller, engraved surfaces may be used for the final pressure treatment to produce an embossed surface.

Example VI A batt weighing about 8 ounces per square yard measuring about 2.3 inches in thickness and composed of 6 denier, 3 nylon staple fibers was immersed in an aqueous 36% ferric chloride solution at C. for one minute. Slight pressure was applied to the batt while wet to consolidate it. The batt was washed with water to remove unreacted ferric chloride. The length and width of the treated batt was substantially the same as the original batt. The dry product was a reddish brown colored sponge-like product capable of absorbing water weighing about eight times its own dry weight. The reddish-brown color can be removed from the product without altering its spongy character by treatment with aqueous hydrochloric acid.

Example VII A Chamois-like product is produced by pressing the dry sponge product of Example VI at about 110 C. and 500 p. s. i. for two minutes. This product has essentially the same properties as the product described in Example ll.

Example VIII A leather-like product is produced by immersing the sponge formed in Example VI in an aqueous 22.8% nitric acid solution at room temperature for one minute, by which time it lost about 40% of its original area. it was washed, dried and hot pressed for two minutes at C. and 500 p. s. i. The final product was similar to that described in Example I except for its reddish-brown color which gave it the appearance of natural leather.

The preferred and operable concentrations and temperatures for the zinc chloride and ferric chloride aqueous baths for the formation of sponge and chamois products are illustrated below:

For the formation of leather-like products the preferred and operable concentrations and temperatures of the aqueous nitric acid bath for treating the sponge product are illustrated below:

Percent: Ooncen- Temperature of tration of Bath Bath, O.

Pre Operable Pre- Operable ferred Range ferred Range N itric Acid 23 In general when the higher concentrations are used the lower temperatures are employed and vice versa.

Generally reduced concentration, temperature or time of immersion in the aqueous baths will result in a lessening of the change brought about in the batt. A treatment that is too weak will result in little or no change in the starting material; excessive conditions often will cause the starting material to dissolve. Judicious adjustment of the conditions to obtain the desired effect is not diificult, however. Pressure for the sponge formation need not be particularly high. Usually a light hand pressure will prove satisfactory. The dry high pressure treatment to compact the product further is optional except in the production of the chamois-like materials.

Thorough and complete washing of the batts after both the metal chloride and nitric acid treatments is necessary since any free metal chloride left in the web causes loss of fiber character, while free nitric acid left in the Web causes enbrittlement and discoloration during subsequent drying operations and/or aging.

In addition to the methods of preparation given above, another additional treatment of the fused and retracted product may be used to weaken the surface fibers and render them less likely to retain a scuff, permitting them instead to break off when subjected to sufiicient abrasion. For this step, immersion in 60% aqueous zinc chlo ride for five seconds at 110 C. is quite satisfactory. Other strong chemical treatments may be chosen by analogy with the normal treatments given above. This kind of treatment may be desirable to harden the softer side of products showing dissimilar characteristics from one surface to another, which may be caused by unequal access to the reagent during processing. Sanding the after-treated product may be useful in preparing a buck-like surface. An additional method for finishing the leather-like product is by heating and pressing one surface near the melting point for a short time against a smooth plate. A thin, flexible, durable and shiny surface may be imparted to the leather-like structures in this way. As indicated in Example V, engraved embossing plates may be used for the final heat and pressure treatment to produce an embossed surface on the leather-like products to simulate natural leather. The well-known abrasion resistance of nylon is a primary factor in assuring the utility of either the normal or aftertreated leather-like products.

The high degree of quality control possible in preparation of sponge, chamois, and leather-like materials according to this invention is a clear advantage over the formation of natural products. No particular limit exists on the external dimensions of the products of this invention. The well-known chemical stability of nylon is a further recommendation for these products. Many other advantages of their manufacture and use will be readily apparent. The leather-like materials alone are useful in a wide range of household and industrial applications, including shoe uppers, upholstery, suitcases, game balls, harness, many forms of apparel, machine belting, and coverings for working surfaces, to name but a few. Many uses for the intermediate products in the formation of finished articles also are obvious.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof and, therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. The process of preparing a fibrous structure which comprises forming a batt of nylon fibers, treating said batt with an aqueous bath containing a metal chloride, said metal chloride being a member of the group consisting of zinc chloride and ferric chloride, the contraction of zinc chloride in the aqueous bath being 30% to and the concentration of ferric chloride being 22% to 42%, the temperature of the zinc chloride bath being 40 C. to 80 C. and the temperature of the ferric chloride bath being 60 C. to 105 C., washing the batt substantially free of unreacted metal chloride and drying.

2. The process of claim 1 in which at least some of the fibers are oriented perpendicularly to both the length and width of the batt.

3. The product of the process of claim 1.

4. The process of preparing a fibrous chamois-like structure which comprises forming a batt of nylon fibers, treating said batt with an aqueous bath comprising a metal chloride, said metal chloride being a member of the group consisting of zinc chloride and ferric chloride, the concentration of zinc chloride in the aqueous bath being 30% to 80% and the concentration of ferric chloride being 22% to 42%, the temperature of the zinc chloride bath being 40 C. to 80 C. and the temperature of the ferric chloride bath being 60 C. to 105 C., washing the batt substantially free of unreacted metal chloride, drying said batt, and pressing and heating the dry batt to reduce its thickness.

5. The product of the process of claim 4.

6. The process of preparing a water vapor permeable fibrous leather-like structure which comprises forming a batt of nylon fibers, treating said batt with an aqueous bath comprising a metal chloride, said metal chloride and ferric chlonde, the concentration of zinc chloride in the aqueous bath being 30% to 80% and the concentration of ferric chloride being 22% to 42%, the temperature of the zinc chloride bath being 40 C. to 80 C. and the temperature of the ferric chloride bath being 60 C. to 105 0., Washing the batt substantially free of unreacted metal chloride, subsequently treating said batt with an aqueous bath comprising 15% to 25% nitric acid to reduce its length and width, the temperature of the nitric acid bath being 20 C. to C., washing the batt substantially free of unreacted nitric acid, drying said batt and pressing and heating said batt to reduce its thickness.

7. The product of the process of claim 6.

OTHER REFERENCES Nylon, Rayon and Synthetic Textiles, May 1950, page 9. 

1. THE PROCESS OF PREPARING A FIBROUS STRUCTURE WHICH COMPRISES FORMING A BATT OF NYLON FIBERS, TREATING SAID BATT WITH AN AQUEOUS CONTAINING A METAL CHLORIDE, SAID METAL CHLORIDE BEING A MEMBER OF THE GROUP CONSISTING OF ZINC CHLORIDE AND FERRIC CHLORIDE, THE CONTRACTION OF ZINC CHLORIDE IN THE AQUEOUS BATH BEING 30% TO 80% AND THE CONCENTRATION OF FERRIC CHLORIDE BEING 22% TO 42%, THE TEMPERATURE OF THE ZINC CHLORIDE BATH BEING 40* C. TO 80* C. AND THE TEMPERATURE OF THE FERRIC CHLORIDE BATH BEING 60* C. TO 105* C., WASHING THE BATT SUBSTANTIALLY FREE OF UNREACTED METAL CHLORIDE AND DRYING. 